The invention relates to liquid filters, and more particularly to a service interval change indicator more accurately reflecting filter life.
Liquid filters, including fuel filters, typically have a vertically axially extending housing having an annular filter element extending axially between top and bottom ends and having an inner hollow interior and an outer annular space between the filter element and the housing. The housing has an inlet to the annular space, and an outlet from the hollow interior. Liquid is filtered by flowing from the annular space through the filter element into the hollow interior. The annular space is viewable through the housing, e.g. through a transparent housing side wall, such that an operator or service technician can see the level of liquid in the annular space as an indication of when to replace the filter element. The higher the level of liquid in the annular space the greater the pressure drop across the filter element and hence the greater the plugging of the filter element.
In many applications, the liquid or fuel level, including the rise thereof in the noted annular space, does not accurately reflect filter life. For example, in one application, fuel level in a clear housing reaches the top with 2xe2x80x3 Mercury, Hg, (68,000 dyne/cm2), restriction, while the filter element is capable of 8xe2x80x3 Mercury (271,000 dyne/cm2), restriction. Hence, using fuel level in the noted annular space of the clear housing as an indicator to change the filter element results in a premature such change. This is objectionable because of the less than full life usage of the filter element, the more frequent filter element changes, and the corresponding higher overall cost thereof.
The invention of the noted parent application addresses and solves the above noted objections. In one aspect, the parent invention delays the rise in liquid level in the noted annular space to correct the otherwise premature indication of a need to change the filter element. In another aspect, liquid level in the noted annular space is allowed to rise to controlled levels providing advance and more accurate indication of a forthcoming need to change the filter element.
The present invention arose during continuing development efforts directed toward liquid filters, including fuel filters, including for diesel fuel, which must provide high removal efficiency and low pressure drop.
As is known, fuel filters are often used on the suction side (low pressure or vacuum side) of the fuel pump. In order to obtain reasonable service intervals without fuel starving the engine, the initial pressure drop should be under 1 inch of Mercury, Hg, (34,000 dyne/(cm2) with a terminal pressure drop across the filter, xcex94P, in the range of 5 to 10 inches of Mercury (170,000 to 340,000 dyne/cm2). Historically, plugged fuel filters are one of the leading causes for on-highway service calls for over-the-road trucks. Typically, the filters are plugged with soft contaminants, e.g., asphaltenes, biological growth, resins, or other sludge-type material, often introduced as a result of fuel transportation and handling. At the same time, truck operators are under economic pressure to reduce costs, including maintenance costs due to scheduled and unscheduled maintenance and replacement filters. It is thus desirable for operators to be able to fully utilize the contaminant-holding capacity of filters (i.e. not change out the filters too soon), without actually plugging the filter and jeopardizing engine operation. To do this, they must be able to accurately detect filter plugging. In the past, a variety of gages and sensors have been utilized to monitor pressure drop across the filter, however these are expensive, not always reliable, and are often ignored by operators. Another common technique is to use air/fuel vapor in the fuel filter housing as a visual indicator of element condition. In the air visualization method, the disappearance of the air is erroneously assumed to be an indicator of filter plugging. The underlying premise for this method is the observation that, in practice, air carried along with the fuel tends to collect in the top of the filter housing. This air pocket is commonly observed with new filters and not with plugged filters. The air visualization method is relatively popular, in that it is inexpensive, easy and, if used regularly, minimizes problems resulting from waiting too long to change the filter. On the other hand, the method is inaccurate and leads to premature, costly filter changes.
The present invention addresses and provides further solutions to the above noted objections. In one aspect, the invention provides an improved air visualization method and mechanism avoiding the above noted source of inaccuracy. In one form, this is accomplished by separating the filtration and indication functions. Various embodiments of the latter are provided.